I found this theory here on tumblr full credit goes to the OP. I'm just copying and pasting it here for us to discuss.

Steven Universe Theory: Rose’s Secret; Where is Pink Diamond?

Rose has been a major mystery in the show, but is she hiding something in front of all of us. Besides her on origins, Rose tends to be the character holding all the secrets of Gem activities and history on earth, even keeping things from her own Crystal Gems, as seen in “ Keeping It Together” where Garnet is surprised to find the shards of Fallen Crystal Gems and claiming that Rose knew and Lied to them. Rose is no stranger to hiding things, but her biggest secret may have been staring us right in the face.First we need to address a theory that has been revolving around the fandom since the Season 1.

Is Rose Pink Diamond? (No, she isn’t)

While there has been subtle nudges to the fandom to spectate that Rose was going to be revealed to be Pink Diamond, but that theory has several issues.- The Reveal of both Blue Diamond and Yellow Diamond shows several astetics that seems to be shared by Diamonds:1) Both Diamonds have a towering Height. In “The Answer”, we see Rose in Blue Diamond’s Court giving us a perspective of her height compared to Regular Gems (as well as Pearl) and Blue Diamond, and While Rose is taller than most of the Gems, Blue Diamond was still visually a Colossus. The same can be Said with Yellow Diamond in “Message Received” as Yellow Diamond stood next to her Pearl and Throne; shadowing both as she stood gigantic.2)Each Diamond has a Diamond Cut shaped Gem.3) Peridot describes Quartz to be Big, loyal Warriors on homeworld,. similar to Amethyst and Jasper. in “When it Rains”. These are just a few of the reasons why Rose wouldn’t be Pink Diamond. (or possibility for)

So who is Rose, and who and where is Pink Diamond?

Theory

(To be speculated on)Rose was the Quartz assigned to Pink Diamond. This can be supported by her advanced fighting style and abilities. It can be speculated that Pink Diamond was the first to go to Earth With her Quartz soldier and Pearl to determined whether Earth would be a good candidate for “Drilling”. During that time, Rose would become familiar with the new world, perhaps even showing Pearl the new point of view creating the foundation of their relationship. It wouldnt be til After Pink Diamond reveals the final plans for the Earth Gem Colony that Rose Quartz became distraught. Perhaps she pleaded and tried to reason with Pink Diamond that Rose did something no Loyal Quartz has ever done, betray her Diamond.Rose would turn Against Pink Diamond and Homeworld, defeating Pink Diamond and beginning her stand for Earth. (this would also be where we see her and Pearl speak as seen in Rose’s Scabbard)That Leaves another question, Where is Pink Diamond.Our only real vision of Pink Diamond is a mural in “It could have been Great.” Some have thought hat Pink Diamond may be Bubbled in the Temple. One could argue that she was shattered a battle. However, there is something of note. If the above is true, Rose Has had her sword and Scabbard for as long as she has been on Earth. Pink Diamond is a powerful foe, and would have to be contained, but bubbling is not the only way to contain a Gem as the tale of Lapis has shown that a Gem can be bound to an object like a mirror, or… a SWORD? While a Long shot theory, a close expectation of Rose’s Sword Noticed what can be a huge reveal. Rose has been associated to, well….Roses. However, we mostly see these Roses Blossoming or the Peddles flying by. However On Rose’s Sword, we see a Rose Bud on the Handle of the Blade. A close look would also she a pink triangle that has been seen to represent both Rose and Pink Diamond. What if inside of this Rose Bud, holds Pink Diamond’s Gem. (Rose buds opening revealing something inside is also a well used television trope)This would be a smart move, for Pink would have to keep her close to make sure that no other Gem would be Able to release her and the full force of the Four Diamonds could affect the resistance. So:-Rose is a Quartz who Betrayed Pink Diamond-Rose could be Holding Pink Diamond Captive in the Sword.Now, if this is the case, it should also be noted…. who has the sword now….As of this moment, if the above turns out to be true, Connie is holding The Sword and unknowingly could also be holding Pink Diamond’s Gem.What are your thoughts?Do you Think Rose and Pink Diamond are separate?Is Pink Diamond being Held in the Sword?What will happen with Connie if Homeworld FInds Out?

No. Interesting theory, but no. Because it leaves one big gaping hole: WHY are like 95% of things related to Pink Diamond, shattered? In the Sky Arena, Pink Diamond's affiliations are shattered. It's like they're trying to wipe out the existence of Pink Diamond in history. So the idea that Rose betrayed Pink Diamond is a big no (and thus cancels out Pink Diamond being in the sword, which yeah is a long shot and most likely won't be the case).

It is still entirely possible that Rose Quartz is Pink Diamond, even if she's smaller than the Diamonds. Why? Because she can shape-shift. She can make her body look however she wants. She could be colossus, too, but hides it for whatever reason. This is still a possibility. Plus, if you look in one of the murals, Rose Quartz is just as big as White Diamond when they are battling.

I stick to the idea of Rose being Pink Diamond because they won't reveal who Pink Diamond was. And we're watching a show about Rose's son. She's a significant gem. I know one of the Crewniverse said "her name is QUARTZ" and all that, but why would someone on the crew make such a huge reveal in a tweet? They wouldn't. I mean, yes it's entirely possible that Rose Quartz is not Pink Diamond, but right now it looks pretty likely that she is.

I can't get on board with some quartz overstepping a Diamond and leading the rebellion. Meaning, I can't get on board with Rose Quartz being a quartz and leading the rebellion and then Pink Diamond's affiliations being shattered. It just doesn't make sense. Because if you get to "Ok, maybe Pink Diamond also didn't want to drill the Earth and loved and respected the Earth", then you're left asking "So why did Rose Quartz lead the rebellion and not Pink Diamond if Pink Diamond was in support of protecting the Earth"? Just doesn't make sense.

I still think it could be a possibility that Rose may have betrayed her. In Ancient Egypt, whoever the new Pharaoh was, they tended to wipe out mention any mention of the previous one. It could be a case here. Victors write the history not the losers.

I could be that she never had the chance. They rose up against her in the Gem war before she could. Besides, its easier to betray someone close to you then plot against someone not of your faction. (Her faction being part of Pink Diamond's court).

But there is a chance when we saw that explosion in lapis' back story it was death of pink Diamond. After all we have no idea what part she played in all this. PD is also only one we have no idea how she could look like. who knows maybe PD was even the one to want to protect Earth and Rose carried on that wish?

Last edited by Goldenevil91 on Sun Jun 05, 2016 12:38 pm; edited 1 time in total

Maybe Pink Diamond betrayed Homeworld at the last moments of the war, which resulted in Homeworld knowing for sure that they can't be beat. It's possible she sacrificed herself or she got corrupted...

However it can't be Lion if he really is a corrupted gem. Lion doesn't have a shown gemstone on his body and the only place where we can't tell is his mane. If I had to guess, and Lion really is a corrupted gem; he's Pink Pearl.

The main problem with all of this is: there's been no mention of Pink Diamond at all. To be fair there's been no mention of White Diamond either, BUT we can rightfully assume that White Diamond was with Yellow Diamond and Blue Diamond. There's been no mentions, whatsoever, of Pink Diamond in this war. Like I said, it's extremely odd that this whole war was led by Rose Quartz alone. Even if there was betrayal, it'd be somewhere in here.

Think about it: If Rose Quartz is indeed NOT Pink Diamond, she'd have been mentioned along with the other diamonds and we would've seen Pink Diamond associated with that final explosion. But we didn't. If Pink Diamond betrayed Homeworld at the last minute, it still would have been said. But the focus is only on Rose.

If Pink Diamond was on Rose's side, we'd have heard that Pink Diamond is leading the rebellion.

They're hiding Pink Diamond from us right now for a reason but whichever side Pink Diamond is...how they're handling it just now logically doesn't make sense because Pink Diamond would have to crop up somewhere because if Rose is NOT Pink Diamond, then she was directly under Pink Diamond.

Crazy idea what if Pink Diamond became a corrupted gem? I mena think about it. If she was on rebellion side she would be treated as it's leader instead of Rose. But if she never betrayed home world she would not be cut out from symbol of diamonds. So what could happen to Diamond to loose their glory enough to be authoritative figure like other 3 diamonds? Corruption.

Even though Rose was made on Earth and is seen to not be one of the Diamonds, maybe all that Pink Diamond symbolism in the structures on Earth is just that; symbolism.

It's entirely possible that Rose was the one in charge on Earth before the war and, while her sphere of influence did not extend to Homeworld, she was a sort of 'diamond' to those on Earth, prompting a pink diamond to be inserted into the Diamond logo.

Pink Diamond was shattered. While all of her structures and statues may have been destroyed because of a betrayal, it could also be the show's way of saying 'hey, yeah, her statues weren't the only ones reduced to shards'. I don't know what part Rose would play in this theory, but whoever Pink Diamond was, the state of her symbols indicate that she's lonnnng gone.

Rose is Pink Diamond. She was made on Earth, yes, but even if she wasn't in power beforehand, maybe she was made to be a Diamond, either to replace an old or shattered PD or to simply lessen the burden on the other Diamonds with Gem Society growing bigger and bigger each day.The fact that Blue and White Diamond were both shown to be on Earth at some point supports this theory (or, in the very least, that something big was happening on Earth); why would half of the Diamond Authority go out of their way to look at a simple Kindergarten and a few gem structures?

Last edited by Swords&Roses on Fri Aug 05, 2016 2:30 pm; edited 1 time in total

It's just so strange, NO ONE mentions her. Even if Pink Diamond was shattered because of betrayal, like if she supported the rebellion, we don't hear about her at all. I mean, you would think someone would mention her, like at least Pearl. You'd think.

The Crewniverse stressed in the Bismuth episode that Rose Quartz did not want to shatter gems. That was the whole conflict of the episode.

The Crewniverse also stressed that the rubies are dumb. Which means, we should seriously take what they say about Pink Diamond with a grain of salt.

Only a diamond can break another diamond. Now, this is Rebecca Sugar's show and she can do anything she pleases, but right now as it stands, only a diamond can break a diamond and unless Rose Quartz is secretly a diamond (like I have been hoping) she can't do it.

I think it was all a set up. Either the other three diamonds framed Rose Quartz or she had some sort of agreement made with Pink Diamond to shatter her because of other reasons. I'm thinking it's more of the former. Perhaps Rose Quartz got to Pink Diamond and she was gonna support the rebellion and the diamonds found out and shattered her and made it look like Rose Quartz did it.

I think this is entirely possible for two reasons:

Pink represents love and compassion. You don't look at the color pink and associate it with something negative. You just, don't.

Ruby told us that Earth was Pink Diamond's colony. I think that much is true. And I think Pink Diamond was also able to see the same things Rose Quartz was able to see in humans. Maybe Pink Diamond even taught her these views and Rose Quartz passed them on to the Crystal Gems/Steven.

I mean I CAN accept Rose Quartz shattering Pink Diamond with some good, hard evidence beyond Pearl crying over the mention of Rose Quartz shattering her. Now THAT is weird but unexplained. Too much is unexplained. Because remember, Pearl is also wearing a space suit with Pink Diamond's symbol on it.

so with the new episode leaking, jasper was saying how rose did something to pink diamond and this has made jasper want to stop at nothing to fight and beat rose. Well remember when this mural was shown, what if rose betrayed pink diamond and poofed her and somehow used the power of her gem to defeat/fight white diamond.

I think that is Pink Diamond that Rose Quartz is holding, but that can't be white diamond. White diamond has her gem on her forehead.

Now, it is possible that Rose harnessed Pink Diamond's power like we see in this mural. I won't write that off just yet. And I still think she is battling White Diamond because of the diamonds surrounding her. However, it can be another quartz gem similar to Jasper that she is battling. It can go either way.

I find the placement of PD's gem to be very interesting, it's in the same spot as Rose Quartz, which leaves two things, either RQ IS PD like we suspect or she's one of several gems that make up PD with Diamonds being fusions. I know these have been said before but given her placement, I find it interesting.